Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $186.65   8.274%   $202.0934   $202.09   $202.10   $202.10  
  Purchase #2 $59.79   9.583%   $65.5197   $65.52   $65.50   $65.50  
  Purchase #3 $202.53   11.687%   $226.1997   $226.20   $226.20   $226.20  
  Purchase #4 $27.37   13.293%   $31.0083   $31.01   $31.00   $31.00  
  Purchase #5 $51.31   12.323%   $57.6329   $57.63   $57.65   $57.60  
  Purchase #6 $162.74   8.419%   $176.4411   $176.44   $176.45   $176.40  
  Purchase #7 $62.98   7.284%   $67.5675   $67.57   $67.55   $67.60  
  7 purchase totals = $753.37       $826.4626   $826.46   $826.45   $826.40